The goal of this research is to contribute to the understanding of the biochemical mechanisms of plaque formation and periodontal disease induction in man. The biosynthesis of plaque-forming polysaccharide will be studied in Actinomyces viscosus, a human oral bacterium which forms plaque and which produces periodontal disease in experimental animals. This proposal deals specifically with the biosynthesis of levan by this organism. On the basis of the requirement of this organism for sucrose to produce levan, and by analogy with other levan- producing micro-organisms, it is expected that levan biosynthesis is catalyzed by a levansucrase. The location (endocellular, exocellular, cell wall-bound) of this enzyme will be determined by differential centrifugation of sonicated cells, using as an assay either the incorportion of radioactive sucrose into levan, or the release of free glucose. The organism will be grown on a number of carbon sources to determine whether the levansucrase is constitutive or inducible. The enzyme will be purified to homogeneity by column chromatography using DEAE-cellulose and hydroxylapatite, and by isoelectric focusing. The enzyme will be characterized with respect to molecular weight, subunits, amino acid and carbohydrate composition, and cofactor requirements. Various agents, such as sucrose analogs, will be tested to block induction and to inhibit levansucrase activity. With a knowledge of the properties and regulation of the levansucrase of A. viscosus, it may be possible to suggest ways of regulating this activity, in vivo. This, in turn, may suggest strategies for the control of plaque formation and the prevention of periodontal disease in man.